1. Field of the Invention
The present invention relates to coaxial cable connectors, and more particularly, to a coaxial cable connector having self-terminating capability when it is uncoupled.
2. Description of Prior Art
Cable lines used for the transmission of high-frequency signals, such as in the range of microwave, often present characteristic impedances. The characteristic impedance is an impedance that would be presented at the input terminals of a transmission line as if the transmission line were infinitely long. For a transmission line having finite lengths, if the end of the transmission line is open circuited, or short circuited, the high-frequency signals that are transmitted through the transmission line would be reflected back from the end to the input end.
To solve the reflection problem, a terminating element having an impedance equal to the characteristic impedance of the transmission line is employed to be coupled at the end of the transmission line to terminate the open circuit. Such a terminated circuit is technically referred to as "a matched circuit" in the art of microwave engineering. A matched circuit would minimize reflections of microwave signals from an interface between two different electrical elements. For transmission lines used in microwave applications, the characteristic impedance thereof is typically 50 .OMEGA.. Therefore, a terminating element having an impedance of 50 .OMEGA., in practice a resistor of 50 .OMEGA., can be used to terminate the transmission line.
Transmission lines for use in microwave applications are often manufactured into coaxial cables having a center conductor surrounded by an insulator and a conducting shield. The conducting shield acts both as a shield of electromagnetic radiation from the center conductor and as a ground.
At the end of such a coaxial cable is there provided a connector for coupling with other installations. An exemplary example of such a connector is illustrated in FIGS. 1A-1B and designated by the numeral "1".
The connector is comprised of a center connecting element 10, an insulator 20, and a casing 30. The center connecting element 10 is connected to the center conductor of the coaxial cable. The casing 30 is made of conductors and connected to the shield of the coaxial cable.
When the coaxial cable is used to connect, for example, a microwave signal generator to a spectrum analyzer, the characteristic impedance of the coaxial cable is matched with impedances built in the spectrum analyzer. However, when the coaxial cable is uncoupled from the spectrum analyzer, the end of the coaxial cable will be left with an open circuit.
Conventionally, as shown in FIGS. 1B-1C, a separate screw-type terminating head 50 can be used to terminate the open-circuited coaxial cable. The terminating head 50 is provided with a resistor 51 having a resistance value equal to the characteristic impedance of the coaxial cable. The resistance value is typically 50 .OMEGA. or 75 .OMEGA.. The terminating head 50 has casing 52 made of conductive material. The resistor 51 is connected to the casing 52 of the terminating head 50. When the terminating head 50 is screwed to the connector the casing 52 thereof is electrically connected with the housing 30 of the connector whereby the end of the center conductor of the coaxial cable is connected via the resistor 51 to the ground. The coaxial cable is thus terminated. Since the terminating head 50 is a separate device, it is often inconvenient to use.
As a consequence, a self-terminating coaxial cable capable of automatically switching the end thereof to a terminated condition when the coaxial cable is left uncoupled is desired. The terminated condition is defined as a condition under which the center conductor of the coaxial cable is connected via an element of matched impedance to the conducting shield of the same.
Among the prior art self-terminating connectors for use with coaxial cables, one type is disclosed in a U.S. Pat. No. 4,575,694 to Lapke et al.